Ancient quasar imaged when the Universe lacked heavy metal

Nothing heavier than helium in the neighborhood.

Composite X-ray/optical/radio image of a quasar: a bright supermassive black hole. Studies of a similar quasar found only neutral hydrogen in the environment, which may help constrain models of the environment in which the first stars formed.

For a few instants after the Big Bang, the Universe was hot and dense enough to fuse hydrogen into helium and lithium. But this period of time was transitory. Heavier elements, including oxygen, carbon, and the like, didn't have time to form; they were the product of stars that only appeared hundreds of millions of years later. Modern galaxies still contain ancient stars with a composition corresponding to early times. However, there is a significant gap in our knowledge: no direct detailed chemical data from the first billion years of the Universe has been available.

Now a study of a quasar from 772 million years after the Big Bang has helped fill in that gap. Robert A. Simcoe and colleagues measured the absorption of light by gas immediately around the quasar, and determined it to be nearly devoid of elements heavier than helium. Their results leave two possibilities. If the hydrogen gas was part of an early galaxy, then it could have been part of the environment in which early (as yet unobserved) stars could form. Alternatively, if the gas was part of intergalactic space, it indicates that the first stars formed somewhat later than many models predicted.

The process of building chemical elements via nuclear fusion is known as nucleosynthesis. During the first few minutes after the Big Bang, conditions were right to produce most of the hydrogen, helium, and lithium in the cosmos, a process called Big Bang nucleosynthesis (BBN). Heavier elements, known (perversely) by astronomers as "metals", were later produced in stars via stellar nucleosynthesis, and distributed into interstellar space as those stars died.

Modern galaxies like the Milky Way contain populations of stars that we can divide based on their metal content. The Sun is a Population I star, with a relatively high metal abundance; older, Population II stars near the galactic center are metal-poor. However, the earliest, metal-free stars—known as Population III—are still hypothetical. According to widely accepted models, Population III stars were massive and therefore short-lived, going supernova and spreading the first metals into interstellar space.

When did these first stars form, and did they actually correspond to our models? These questions are still unanswered. The crucial period of time when the first stars must have formed is still marked by a paucity of data.

The researchers in the present study used the Baade telescope, one of the twin Magellan telescopes at the Las Campanas Observatory in Chile. They analyzed the infrared spectrum of the quasar ULAS J1120+0641, which emitted its light 772 million years after the Big Bang. (Quasars are bright beams of light emitted by supermassive black holes; they are some of the only objects that can be seen at such vast distances.)

Comparing the predicted spectrum of an ideal quasar to that of ULAS J1120+0641, the astronomers found an anomalously large amount of hydrogen absorption from neutral hydrogen atoms in the quasar's immediate environment, and no significant indication of metals.

The unusual aspects of the spectrum indicate either a high density of neutral hydrogen very close to the quasar, or a more diffuse cloud around it. These options carry very different implications. If the hydrogen is close to the supermassive black hole, then it likely was part of a protogalaxy: a collapsing cloud of gas and dark matter that would eventually form a galaxy. In that case, the total environment would be conducive to the formation of Population III stars (though the Magellan data would not be sufficient to observe them).

On the other hand, if the neutral hydrogen formed a diffuse cloud, then it would suggest the first stars didn't form until a later date. If stars were already present at the time the quasar emitted this light, their output would ionize the hydrogen, changing the absorption spectrum.

Of course, one quasar doesn't provide a definitive case study of the entire environment 772 million years after the Big Bang. The earliest stars didn't all form at once, so it's unwise to extrapolate from this one quasar to the entire early Universe. Nevertheless, this observation provides an interesting preliminary case study, bringing us closer to a picture of the environment in which the first stars formed.

Wow, it's a strange, Brave New World with such X-Factors located far off in space and Somewhere In Time. It certainly gives me Piece of Mind to know that my Fear of the Dark is allayed even out on the very edges of the Final Frontier, though I guess it's not a Matter of Life and Death.

The universe had to be a very, very small fraction of it's current size back when these stars formed otherwise how would there be enough metals out there to constitute the vast number of stars and galaxies in the present universe (this includes the parts of the universe we can't see)? Either that or there were a heck of a lot of Pop III stars present in the early universe. Could the "metal" explosion experienced after most of these Pop III stars died contributed to the faster inflation of the universe? The amount of baryonic matter available is truly mind-boggling and that's just a small percentage of the "stuff" the universe is made up of.

Wow, it's a strange, Brave New World with such X-Factors located far off in space and Somewhere In Time. It certainly gives me Piece of Mind to know that my Fear of the Dark is allayed even out on the very edges of the Final Frontier, though I guess it's not a Matter of Life and Death.

How can the entire universe compressed into a tiny space not have enough heat to generate all those metals? I mean, if a single sun is sufficient, how can all of existence not be? Is it just because it expanded too fast?

How can the entire universe compressed into a tiny space not have enough heat to generate all those metals? I mean, if a single sun is sufficient, how can all of existence not be? Is it just because it expanded too fast?

Big Bang nucleosynthesis began a few minutes after the big bang, when the universe had cooled down sufficiently to allow deuterium nuclei (one proton + one neutron) to survive disruption by high-energy photons.

However, the earliest, metal-free stars—known as Population III—are still hypothetical. According to widely accepted models, Population III stars were massive and therefore short-lived, going supernova and spreading the first metals into interstellar space.

I'm a bit confused here. If these hypothetical Population III stars were "metal-free", how did they spread the first metals into space when going supernova?

However, the earliest, metal-free stars—known as Population III—are still hypothetical. According to widely accepted models, Population III stars were massive and therefore short-lived, going supernova and spreading the first metals into interstellar space.

I'm a bit confused here. If these hypothetical Population III stars were "metal-free", how did they spread the first metals into space when going supernova?

How can the entire universe compressed into a tiny space not have enough heat to generate all those metals? I mean, if a single sun is sufficient, how can all of existence not be? Is it just because it expanded too fast?

Big Bang nucleosynthesis began a few minutes after the big bang, when the universe had cooled down sufficiently to allow deuterium nuclei (one proton + one neutron) to survive disruption by high-energy photons.

Thanks for the link, that cleared things up. Despite having seen lots of (not technical) material about the big bang, the speed of expansion just boggles my mind. It was only the right temp for creating heavier elements for 17 minutes? Wow.

Wow, it's a strange, Brave New World with such X-Factors located far off in space and Somewhere In Time. It certainly gives me Piece of Mind to know that my Fear of the Dark is allayed even out on the very edges of the Final Frontier, though I guess it's not a Matter of Life and Death.

Iron Maiden takes on a new realm of knowledge: Cosmology!

After all they are well regarded for their promotion of literature and history from both students and teachers.

Weight is an irrelevant concept in the absence of gravity, or at least where gravity is so close to zero that it may be considered negligible. If we assume that the gases are close enough to the quasar, though, and both clouds are equidistant from the quasar, then weight may be something we can talk about. But first we need to know the amount of each gas we're talking about if we want to compare weight. Otherwise, you could say, like my 6th grade physical science teacher used to ask, "Which is heavier? A pound of gold or a pound of feathers?" They both weigh the same: 1 pound! In the absence of a defined amount of each gas, we can only talk about the density of each gas assuming each is subjected to the same pressure and temperature, in which the question should be "What else is less dense than helium?" rather than "What else is lighter than helium?" If we accept the modified question as the version that was intended, then atom-for-atom hydrogen and positronium are both correct answers.

Weight is an irrelevant concept in the absence of gravity, or at least where gravity is so close to zero that it may be considered negligible. If we assume that the gases are close enough to the quasar, though, and both clouds are equidistant from the quasar, then weight may be something we can talk about. But first we need to know the amount of each gas we're talking about if we want to compare weight. Otherwise, you could say, like my 6th grade physical science teacher used to ask, "Which is heavier? A pound of gold or a pound of feathers?" They both weigh the same: 1 pound! In the absence of a defined amount of each gas, we can only talk about the density of each gas assuming each is subjected to the same pressure and temperature, in which the question should be "What else is less dense than helium?" rather than "What else is lighter than helium?" If we accept the modified question as the version that was intended, then atom-for-atom hydrogen and positronium are both correct answers.

Actually, a pound of feathers weighs more than a pound of gold. Feathers are measured in avoirdupois pounds of 16 imperial ounces each (so a pound weighs about 4.448 newtons), while gold is measured in troy pounds of 12 troy ounces each (so a pound weighs about 3.6603 newtons).

Pedantry aside, it is common to refer to relative density as lighter or heavier. In contexts where it makes a difference, researchers clearly spell out what they mean.

Weight is an irrelevant concept in the absence of gravity, or at least where gravity is so close to zero that it may be considered negligible.

In physics/astronomy, gravity varies so greatly by location (should be obvious) that colloquially the terms "heavier/lighter" refer to mass. If someone wants to discuss the effects of a gravitational field, they'll tell you. No need for pedantry.

pusher robot wrote:

Wow, it's a strange, Brave New World with such X-Factors located far off in space and Somewhere In Time. It certainly gives me Piece of Mind to know that my Fear of the Dark is allayed even out on the very edges of the Final Frontier, though I guess it's not a Matter of Life and Death.

I guess we're all Strangers in a Strange Land? Or a Sea of Madness, if you prefer, as space seems to go From Here to Eternity -- a New Frontier out to The Edge of Darkness, beyond our Wildest Dreams. And these quasars are clearly of a far Different World than we inhabit... Brighter Than a Thousand Suns, they could easily make you feel Starblind. But they may help us unlock the history of nucleosynthesis, and understand the origins of Sun and Steel.

Wow, it's a strange, Brave New World with such X-Factors located far off in space and Somewhere In Time. It certainly gives me Piece of Mind to know that my Fear of the Dark is allayed even out on the very edges of the Final Frontier, though I guess it's not a Matter of Life and Death.

I guess we're all Strangers in a Strange Land? Or a Sea of Madness, if you prefer, as space seems to go From Here to Eternity -- a New Frontier out to The Edge of Darkness, beyond our Wildest Dreams. And these quasars are clearly of a far Different World than we inhabit... Brighter Than a Thousand Suns, they could easily make you feel Starblind. But they may help us unlock the history of nucleosynthesis, and understand the origins of Sun and Steel.[/quote]